1. Field of the Invention
The present invention relates generally to gear type transmission apparatus for use in vehicles, and more particularly, to a gear type transmission for a vehicle in which a novel change gear control mechanism including a control rod and a shift rod is employed.
2. Description of the Prior Art
As known conventionally, in a transmission of the gear type for use in a vehicle, a plurality of gear trains each having a different gear ratio and arranged between an input shaft and an output shaft, and a plurality of shift rods selectively connected with a gear shifting lever to be made operative are provided, and one or more of the gear trains are selected, through a shift fork mechanism and a synchronising mechanism, by means of manipulation of the gear shifting lever causing one or more shifting rods to operate selectively, to be operative to transmit power from the input shaft to the output shaft. In connection with such a transmission of the gear type, there has been proposed to support the shift rods by a cover member which is provided for covering an opening formed at an upper portion of a transmission case in which the input shaft, output shaft, gear trains, shift rods and so on are contained, as disclosed, for example, in the Japanese utility model application published before examination under publication No. 56/62458.
FIG. 1 shows schematically a part of a transmission in which shift rods are provided in the manner thus proposed previously. In FIG. 1, a transmission case 100 is provided at an upper portion thereof with an opening 101 and a cover member 102 disposed on the upper portion to cover the opening 101. The cover member 102 is provided at front and rear end portions thereof with bearings 103 and a shift rod 104 is supported at both end portions thereof by the bearings 103 so as to be contained in the cover member 102. In such a case, the shift rod 104 can be easily mounted on the transmission by causing the shift rod 104 to engage with the bearings 103 to be attached to the inside of the cover member 102 and then mounting the cover member 102 which is accompanied with the shift rod 104 on the upper portion of the transmission case 100 to cover the opening 101.
However, in the event of the structural arrangement as shown in FIG. 1, since the bearings 103 are provided at the front and rear end portions of the cover member 102 for supporting the shift rod 104, the shift rod 104 is positioned above a contacting face 105 which is formed at a lower end portion of the cover member 102 for coming into contact with an upper end face of the transmission case 100 which surrounds the opening 101. Accordingly, the height (h.sub.1) of the cover member 102 measured from the contacting face 105 becomes relatively large and therefore a major portion 100b of the transmission containing the gear trains and located behind a clutch housing 100a is arranged to be relatively tall. This results in a problem that a vehicle to which the transmission is applied is required to have a floor which is so raised as to restrict a cabin space formed in the vehicle.
For avoiding the problem mentioned above, it has been further proposed, as shown in FIG. 2, to support a shift rod 104' by a bearing 103' which is provided at the inside of a cover member 102' to project from the cover member 102' downward so as to be lower than a contacting face 105' formed at a lower end portion of the cover member 102' for coming into contact with an upper end face of a transmission case 100'. With such a configuration, the shift rod 104' can be positioned to be at the same level as the contacting face 105' or lower than the contacting face 105', and therefore the height (h.sub.1 ') of the cover member 102' measured from the contacting face 105' is reduced.
However, in the case where such a structural arrangement shown in FIG. 2 is employed, since the bearing 103' which projects from the inner surface of the cover member 102' is a hindrance to the movement of a tool for processing the contacting face 105' of the cover member 102', it is difficult to process the contacting face 105' of the cover member 102' with sufficient precision. Consequently, it is feared that undesirable minute gaps are formed between the contacting face 105' of the cover member 102' and the upper end face of the transmission case 100' and therefore a matched portion between the contacting face 105' of the cover member 102' and the upper end face of the transmission case 100' is not provided with proper sealing performance, so that oil contained in the transmission leaks out of the transmission case 100'.
Further, in the case where the gear shifting lever is provided at the rear portion of the transmission, there has been also proposed to use a control rod provided between the shift rods and the gear shifting lever for connecting therethrough each of the shift rods with the gear shifting lever, as disclosed, for example, in the Japanese utility model application published before examination under publication No. 55/40416.
FIG. 3 shows schematically a part of a transmission in which the control rod is provided in the manner proposed previously as mentioned above. In FIG. 3, a control rod 112 is provided between a plurality of shift rods 110 (one of the shift rods 110 is shown in FIG. 3) and a gear shifting lever 111. A rear end portion of the control rod 112 is coupled with a lower end portion of the gear shifting level 111 through a coupling member 113 fixed on the control rod 112, and a front end portion of the control rod 112 is connected through a gate mechanism 114 with a rear end portion of one of the shift rods 110 selectively for causing the shift rod 110 to be in operation. The gate mechanism 114 comprises a projection 112a provided at the front end portion of the control rod 112 to protrude upward and a depression 110a formed at the rear end portion of each shift rod 110. The projection 112a is moved to swing in accordance with the rotation of the control rod 112 caused through the manipulation of the gear shifting lever 111 so as to engage with the depression 110a formed on each shift rod 110 and thereby make one of the shift rods 110 become operative selectively.
In the transmission provided with the gate mechanism 114 as described above, the top of the projection 112a protruding upward from the front end portion of the control rod 112 is caused to engage with the depression 110a formed at the rear end portion of each shift rod 110 to look downward and positioned above, and therefore the height (h.sub.2) of the gate mechanism 114 measured from an axis of the control rod 112 becomes considerably large. This results in the disadvantage that the transmission is inevitably shaped to be relatively tall and consequently a vehicle to which the transmission is applied is required to have a floor which is so raised as to restrict a cabin space formed in the vehicle.
In the case where a couple of shift rods are provided, the height h.sub.2 of the gate mechanism 114 can be reduced by means of arranging the depression formed at the rear end portion of each shift rod to be sideways. However, in the event of three shift rods, as shown in FIG. 4, although each of depressions 115a formed on both side shift rods 115 is able to be made sideways, a depression 116a formed on a central shift rod 116 is unavoidably caused to look downward. Therefore, a portion 116b of the central shift rod 116 disposed on the depression 116a protrudes upward and, as a result, the height (h.sub.2 ') of the gate mechanism can not be reduced.